Electrocatalysts for the oxygen reduction reaction (ORR) play a crucial role in renewable-energy technologies, including metal-air batteries and fuel cells. However, development of novel catalysts with high activity and low cost remains a great challenge. Here, we present hierarchical MnO2/reduced graphene oxide (MnO2/rGO) hybrid nanosheets by using a facile method and study its electrocatalytic performance. Cyclic voltammograms, and rotating disk electrode and rotating ring/disk electrode measurements demonstrate that the hierarchical MnO2/rGO hybrid nanosheets exhibit excellent electrocatalytic activity for the ORR in an alkaline medium, as evidenced by their higher cathodic current density, more positive onset potential, lower H2O2 yield, and higher electron transfer number compared to pure rGO. The excellent catalytic activity of the MnO2/rGO hybrid nanosheets highlights the importance of the synergetic chemical coupling effect between the ultrathin MnO2 nanosheets and the graphene layer.